How is the sky130 merged lef generated?

[UditDey]

Hi, I've just started experimenting with OpenROAD and I'm going through the flow scripts to understand how the tool works. I have a sample netlist and I've compiled the sky130 library and I'm seeing and copying how the flow scripts work with this library.

I downloaded the sky130 PDK and ran make timing which generated the liberty standard cell timing files. However there is no merged standard cell LEF file. I saw that the flow scripts have a merged LEF for sky130 in flow/platforms/sky130hs/lef/sky130_fd_sc_hs_merged.lef and I was curious about how this merged LEF was made from the individual cell LEFs. There seems to be no makefile target in the PDK to generate it

[maliberty]

It is a foundry provided file that is part of the PDK; it is not generated by openroad.

[UditDey]

Yes but the sky130 PDK that I downloaded from the repo and setup doesn't have a merged LEF. It seems to have only the individual LEFs for each cell. make timing generates liberty files but not a merged LEF file or anything like that

Just to reiterate, I'm asking this just to learn more about this stuff. I apologize if I miss something basic etc

[maliberty]

It happened years ago at the very start of skywater support so I don't really know. I'm don't think we even created that file but just imported it. It might have been Google or EFabless. I would guess a simple script to strip the common header and concatenate them. @msaligane do you know (you have the first commit)?

[mguthaus]

The skywater PDK was created with separate files to:
a) reduce max file size
b) group related info into a per cell directory

This was thought to create more flexibility, but it requires you to "install" the PDK. When you "install" the PDK, it should create the merged file formats like LEF, lib, etc.

[mguthaus]

By the way, you are better off installing through open_pdks which also has bug fixes that are not merged into the upstream Sky130 repo. I'm not sure why they don't accept those changes after all these years still...

https://github.com/RTimothyEdwards/open_pdks

[maliberty]

They have no CI and practically they have moved on. I think open_pdk is the de facto distribution.